Air driven sander



Dec. 4, 1956 G. A. LARsoN AIR DRIVER SANDER Filed Nay 14. 1954 2 n WN y o E w, w.. M r zw l 5 17| yf i. Ge 4. j 6 MW w ww y ed y* Hl mw 275 w a y@ 5 m l@ u l@ n( I L2; 5

AIR DRIVEN SANDER George A. Larson, Rockford, lll.; Alice R. Larson, executrix of said George A. Larson, deceased, assigner to Alice R. Larson, Rockford, Ill.

Application May 14, 1954, Serial No. 429,868

16 Claims. (Cl. 121-3) This invention relates to air-driven portable sanders having reciprocating type motors similar to that disclosed in the copending application of Arvid G. Larson, Serial No. 271,775, tiled February 15, 1952, which resulted in Patent No. 2,681,042, issued lune 15, 1954.

The principal object of my invention is to generally improve the design and construction of the device disclosed in the aforesaid copending application with a view to more economical production and assembly thereof.

Another object is to provide a sander of the kind mentioned so constructed that the reciprocating element to which the pad holder is attached acts like an exhaust valve and allows the exhaust air to escape around its opposed reduced end portions at `the ends of the strokes, thereby expelling any dust, dirt or bits of abrasive that might otherwise collect around the opposite ends of the bearing in which the reciprocating element operates and thus prevent their finding their Way into the bearing and air motor and interfere with the free and easy operation of the device besidescausing excessive wear.

T hev invention is illustrated in the accompanying drawing, in which- Fig. 1 vis a longitudinal section in a vertical plane on the line 1-1 of Fig. 2 through a sander made in accordance with my invention;

Fig. 2 is a longitudinal section in a horizontal plane on the line 2 2 of Fig. 1, and

Fig. 3 is a cross-section on the line 3 3 of Fig. 1.

The same reference numerals are applied to corresponding parts throughout these views.

Referring to the drawing, the motor indicated by the reference numeral 5 is generally similar to that disclosed in the aforesaid patent and comprises a cylinder 6 in which a single elongated piston 7 is reciprocable. Slidable in the opposite ends of the cylinder 6 are two cup-shaped valves 8 and 9 which are normally urged inwardly by coiled compression springs 10 and. 11, respectively, the latter being backed up by end plates 12 and 13, respectively, fastened by means of screws 14 onto opposite ends 'of the cylinder 6. Bushings 15, which have reduced ends 16 entered in the opposite ends of the cylinder 6 to serve as bumpers for the valves 8 and 9, are received in counterbores 17 provided therefor in the end plates 12 and 13 and have the springs 10 and 11 extending therethrough for abutment with the plates 12 and 13. Intake ports 18 and -19 are provided in the wall of the cylinder 6 near the opposite ends thereof communicating with annular internal grooves 18 and 19', respectively, provided in the bore of the cylinder. Spaced inwardly from the intake ports 18 and 19 relative to the ends of the cylinder 6 are exhaust ports 20 and 21 which communicate with annular internal grooves .20' and 21 provided `in the bore of the cylinder. The annular grooves 18-19' facilitate inlet of compressed air to the bore, and grooves 20-21 facilitate the exhausting of air circumferentiallyof the cylinder wall. ',.The'two intake ports 18 and 19 are interconnected by a longitudinal passage 22 provided in the wall'of the'cylinder 6, and an L-shaped passage 23 VUnited States Patent O 2,772,663 Patented Dec. 4, 1956 ICC is provided in the end plate 13 communicating with one end of passage 22 and establishing communication therefor with an inlet chamber 24 provided in the end plate 13 to which compressed air is supplied through an inlet nipple 25 whenever the trigger-controlled ball-valve 26 is opened.

In operation, assuming compressed air is admitted to chamber 24 by reason of the opening of valve 26, the piston 7 is moved to the right, moving valve 9 with it. This forward movement of the piston continues until exhaust port 20 is uncovered, whereupon the pressure behind the piston 7 in the cylinder 6 drops instantly to a point where the spring 10 is strong enough to move valve 3 forward, shutting off intake port 18. At this point, valve 9 uncovers intake port 19, and, inasmuch as exhaust port'21 is then covered by piston 7, the piston is moved to the left on the return stroke, duplicating the same sequence with valve 9 as previously occurred with valve 8, and the operations described are repeated over and over again. The springs 10 and 11 are not strong enough to move the piston 7 especially when the piston is operatively connected, as shown, by means of the pin 27 with the reciprocable slide valve element 28 that is connected with and operates the pad-holder 29. These springs 10-11 are furthermore light enough in loading in relation to the air pressure employed to permit operation of the valves 8 and 9 in the manner described, each of the valves remaining in retracted position under air pressure, as described, until the piston 7 is moved forward far enough to uncover the exhaust port 20 or 21 as the case may be. The vent holes 30 provided in the end plates 12 and 13 allow free inlet and outlet of air so that there is nothing to interfere with freedom of reciprocation of the valves 8 and 9. The opposite ends of the piston 7 are chamfered, as indicated at 7', so as to allow compressed air toenter between the end of the piston and whichever one of the valves is operative at the start of a stroke.

The pin 27 providing connection for the piston 7 with the pad-holder 29 is slidable back and fo-rth in an elongated slot 31 provided in the wall of the cylinder 6, an elongated boss 32 being formed integral with the wall of the cylinder and having the slot 31 extending through this boss radially from the bore of the cylinder. The slot 31 intersects and extends diametrically with respect to a bearing opening 33.provided longitudinally in the boss 32, and the reciprocable slide valve element 28 previously mentioned operates in this bearing, so that element 28 disposed in the bearing serves to close the slot and prevent entry to the bore of the cylinder of dust, dirt and bits of grit during the sanding operation. Holes 34 and 35 are drilled through the boss 32 radially with respect to cylinder 6 and the inner ends of these holes provide the exhaust ports 20 and 21 previously mentioned. When the piston 7 reaches the end of a stroke and uncovers one of these exhaust ports, as, for example, is true of port 21 in Fig. 1, compressed air is exhausted through the hole communicating therewith, namely, hole 35. The reciprocable slide valve element 28 has annular grooves 36 provided externally thereof on the opposite end portions, and these grooved portions 36 allow the air to escape through hole 34 or 35, whichever happens to be then functioning as the exhaust opening, the greater portion of the air, however, escaping through the adjacent end of bore 33 around the reduced end portion 36 of element 28. In that way any dust, dirt or bits of abrasive that might be in the air as a result of the sanding operation and might otherwise collect around the ends of the bearing 33 and on top ofthe pad holder 29 will surely be blown away. There is no danger, therefore, of such foreign matter finding its way into the bore 33 and eventually into the bore of the cylinder 6 and interfering with the free and easy operation of the device, besides causing excessive wear.

A channel-shaped handle 37 straddles the cylinder 6, as most clearly appears in Fig. 3, and is hollowed out lengthwise on the outer sides thereof, as indicated at 38, to provide finger recesses to facilitate gripping the sander in guiding it on the work being sanded. The flat end surfaces 39 of the handle 37 have abutment with the fiat surfaces 40 on the inner side of the end plates 12 and 13 to hold the handle 37 in place when the end plates are fastened to the cylinder. Therefore, it requires only a single large screw 41 at the middle of the top of the handle to fasten the handle to the cylinder 6. A bushing 42 is entered with a slip fit through a radial hole 43 in the handle 37 and threaded in a registering radial hole 44 provided in the wall of the cylinder 6, and this bushing 42 is internally threaded to receive a screw 41, the head of which enters an enlargement or counterbore 45 in the outer end of the hole 43. An oil hole 46 is provided in the inner end of the bushing 42 and a screen 47 covers the hole to prevent foreign matter from entering the bore of the cylinder, and felt or the like is placed over this screen, as indicated at 48, and serves to hold a supply of oil to furnish lubricant in small amounts to the piston 7 for long periods of operation in the bore in cylinder 6, the screw 41, of course, functioning to keep the felt 48 in place and compress it slightly.

The trigger 49 overlying one end of the handle 37 and the top of the end plate 13 is suitably pivoted at one end to the handle 37 by means of a cross-pin 50 and has its other end free and engaging the upper end of a pin 51 slidable in a bore in a bushing 52, the lower end portion of which is cut away externally to define the air inlet chamber 24 previously mentioned, besides providing a seat for the ball valve 26 that is normally urged into engagement with the seat by means of a coiled compression spring 53.

It is believed the foregoing description conveys a good understanding of the objects and advantages of my invention. The appended claims have been drawn to cover all legitimate modifications and adaptations.

I claim:

l. A reciprocating air motor comprising a cylinder having air inlet ports spaced inwardly from the opposite ends and air outlet ports spaced farther inwardly from said ends, a piston reciprocable in said cylinder, valves slidable as pistons relative to and adapted to cover and uncover the intake ports alternately and arranged to be engaged and moved outwardly by thepiston, spring means normally Iurging said valves inwardly, a secondary cylinder in spaced parallel relation to the first mentioned cylinder having air exhaust ports spaced inwardly from the Opposite ends communicating with said outlet ports, a slide reciprocable in said secondary cylinder and adapted to cover and uncover said exhaust ports alternately, and means connecting said piston and slide to reciprocate in unison.

2. A reciprocating hand tool comprising a cylinder having air inlet ports spaced inwardly from the opposite ends and air outlet ports spaced farther inwardly from said ends, a piston reciprocable in said cylinder, valves slidable as pistons relative to and adapted to cover and uncover the intake ports alternately and arranged to be engaged and moved outwardly by the piston, spring means normally urging said valves inwardly, a secondary cylinder in spaced parallel relation to the first mentioned cylinder having air exhaust ports spaced inwardly from the opposite ends communicating with said outlet ports, a slide reciprocable in said secondary cylinder and adapted to cover and uncover said exhaust ports alternately, means connecting said piston and slide to reciprocate in unison, and a work engaging device adapted to be reciprocated with said piston and slide operatively connected with said slide.

3. A reciprocating sander and rubber comprising a cylinder having air inlet ports spaced inwardly from the opposite ends and air outlet ports spaced farther inwardly from said ends, a piston reciprocable in said cylinder, valves slidable as pistons relative to and adapted to cover and uncover the intake ports alternately and arranged to be engaged and moved outwardly by the piston, spring means normally urging said valves inwardly, a secondary cylinder in spaced parallel relation to the first mentioned cylinder having air exhaust ports spaced inwardly from the opposite ends communicating with said outlet ports, a slide reciprocable in said secondary cylinder and adapted to cover and uncover said exhaust ports alternately, means connecting said piston and slide to reciprocate in unison, and an elongated pad holder adapted to be reciprocated with said pi-ston and slide operatively connected at its opposite ends with the opposite ends of said slide, which extend from the ends of the second named cylinder.

4. A reciprocating sander and rubber comprising a cylinder having air inlet ports spaced inwardly from the opposite ends and air outlet ports spaced farther inwardly from said ends, a piston reciprocable in said cylinder, valves slidable as pistons relative to and adapted to cover and uncover the intake ports alternately and arranged to be engaged and moved outwardly by the piston, spring means normally urging said valves inwardly, a secondary cylinder in spaced parallel relation to the first mentioned cylinder having air exhaust ports spaced inwardly from the opposite ends communicating with said outlet ports, a slide reciprocable in said secondary cylinder and adapted to cover and uncover said exhaust ports alternately, means connecting said piston and slide to reciprocate in unison, and an elongated pad holder adapted to be reciprocated with said piston and slide operatively connected at its opposite ends with the opposite ends of said slide, which extend from the ends of the second named cylinder, the end portions of said slide including portions of reduced diameter which define annular exhaust passages between the end portions of said slide and the end portions of said cylinder communicating with the exhaust ports, whereby the exhaust air is directed outwardly onto opposite ends of said pad holder.

5. A reciprocating air motor comprising a cylinder having air inlet and exhaust ports at its opposite ends, valves slidable as pistons relative to and serving to close and open said ports to admit air under pressure alternately to opposite ends of the cylinder while allowing air to escape from the other end, spring means normally urging said valves in one direction, a double-acting piston reciprocable in said cylinder under pressure of the air admitted alternately to opposite ends of said cylinder, said piston being arranged in its reciprocation to operate said valves against the action of said spring means, a secondary cylinder in spaced parallel relation to the first mentioned cylinder, and a slide reciprocable in said secondary cylinder connected with said piston to reciprocate in unison therewith, said exhaust ports communicating with the opposite ends of the secondary cylinder and arranged to be opened and closed alternately by said slide in the reciprocation thereof.

6. A reciprocating hand tool comprising a cylinder having air inlet and exhaust ports at its opposite ends, valves slidable as pistons relative to and serving to close and open said ports to admit air under pressure alternately to opposite ends of the cylinder while allowing air to escape from the other end, spring means normally urging said valves in one direction, a double-acting piston reciprocable in said cylinder under pressure of the air admitted alternately to opposite ends of said cylinder, said piston being arranged in its reciprocation to operate Vsaid valves against the action of said spring means, a secondary cylinder in spaced parallel relation to the first mentioned cylinder, a slide reciprocable in said secondary cylinder connected with said piston to reciprocate in unison therewith, said exhaust ports communicating with the opposite ends of the secondary cylinder and arranged to be opened and closed alternately by said slide in the reciprocation thereof, and a work engaging device adapted to be reciprocated with said piston and slide operatively connected with said slide.

7. A reciprocating sander and rubber comprising a cylinder having air inlet and exhaust ports at its opposite ends, valves slidable as pistons relative to and serving to close and open said ports to admit air under pressure alternately to opposite ends of the cylinder while allowing air to escape from the other end, spring means normally urging said valves in one direction, a double-acting piston reciprocable in said cylinder under pressure of the air admitted alternately to opposite ends of said cylinder, said piston being arranged in its reciprocation to operate said valves against the action of said spring means, a secondary cylinder in spaced parallel relation to the first mentioned cylinder, a slide reciprocable in said secondary cylinder connected with said piston to reciprocate in unison therewith, said exhaust ports communicating with the opposite ends of the secondary cylinder and arranged to be opened and closed alternately by said slide in the reciprocation thereof, and an elongated pad holder adapted to be reciprocated with' said piston and slide operatively connected at its opposite ends with the opposite ends of said slide, which extend from the ends of the second named cylinder.

8. A reciprocating sander and rubber comprising a cylinder having air inlet and exhaust ports at its opposite ends, valves slidable as pistons relative to and serving to close and open said ports to admit air under pressure alternately lto opposite ends of the cylinder while allowing air to escape from the other end, spring means normally urging said valves in `one direction, a double-acting piston reciprocable in said cylinder under pressure of the air admitted alternately to opposite ends of said cylinder, said piston being arranged in its reciprocation to operate said valves -against the action of said spring means, a secondary cylinder in spaced parallel relation to the rst mentioned cylinder, a slide reciprocable in said secondary cylinder connected with said pistonV to reciprocate in 'unison therewith, said exhaust ports communicating with the opposite ends of the secondary cylinder and arranged to be opened and closed alternately by said slide in the reciprocation thereof, and an elongated pad holder adapted t-o be reciprocated with said piston and slide operatively connected at its opposite ends with the opposite ends of s-aid slide, which extend from the ends of the second named cylinder, the end portions -of said slide including portions of reduced diameter which define annular exhaust passages between the end portions of said slide and the end portion-s of said cylinder communicating with the exhaust ports, whereby the exhaust air is directed outwardly onto opposite ends of said pad holder.

9. A portable air driven sander comprising an elongated cylinder block having a cylinder bore extending lengthwise therethrough, said block having inlet ports spaced inwardly .from the opposite ends and exhaust ponts spaced farther inwardly from said ends, a piston reciprocable in said cylinder and adapted to cover and uncover the exhaust ports alternately, valves slidable as pistons in the opposite ends of said bore relative to and adapted to cover and uncover the intake ports alternately and arranged to be engaged and moved outwardly by the piston, spring means normally urging the valves inwardly, an elongated handle of inverted channel shaped cross-section open at opposite ends straddling said cylinder block and providing passages between the inner side thereof and the outside of said cylinder block which communicate with the exhaus-t ports so as to direct exhaust air out of the open bottom of said handle, end plates fastened .to `and closing the opposite end-s of said handle and secured also to the cylinder block covering the opposite ends of the cylinder bore and serving as abutments for the spring means urging the valves inwardly, 4and .a pad holder reciprocable beneath 4the open bottom lof said handle and operatively-connected with said piston to reciprocate in unison with it.

10. A portable air driven sander comprising an elongated cylinder block having a cylinder bore extending lengthwise therethrough, said block having inlet ports spaced inwardly from the opposite ends and exhaust ports spaced farther inwardly from said ends, a piston reciprocable in said cylinder and adapted to cover and uncover the exhaustv ports alternately, valves slidable as pistons in the opposite ends of said lbore relative to and adapted to cover and uncover Ithe intake ports alternately and arranged to be engaged and moved outwardly by the piston, spring means normally urging the valves inwardly, an elongated handle Iof inverted channel shaped cross-section straddling said cylinder block and secured thereto, said cylinder block having a downward extension within the channel of said handle Iin which a secondary cylinder bore is provided in spaced parallel relation to the tirst mentioned bore, the exhaust ports of said first mentioned bore communicating with ports in the opposite ends of said secondary cylinder bore, a slide reciprocable relative to said ports in said secondary bore to cover and uncover the same and having portions extending trom the opposite endsof said bore, means connecting the piston and slide to reciprocate in unison, and an elongated pad holder reciprocable beneath the open bottom of said handle and operatively connected at its opposite ends with the projecting endsI of said slide so as to reciprocate in unison therewith. Y

1l. A p-ortable air driven sander comprising an elongated cylinder block having `a cylinder vbor'eextending lengthwise therethrough, said block having' inlet ports spaced inwardly from the opposite ends and exhaust ports spaced lfart-her inwardly from said ends, a piston reciprocable in said cylinderland :adapted to cover and uncover the exhaust ports alternately, valves slidable as pistons in the opposite ends of said bore -relative to and adapted to cover Ianduncover the Iintake ports alternately and arranged to be engagedand moved outwardly 4by the piston, springl'means normaly urging the valves inwardly, an elongated handle of inverted channel shaped cross-section straddling said cylinder block' and secured thereto, said cylinder block having a downward extension 'cf elongated form but shorter length than said cylinder block having its ends spaced inwardlyalike from both ends of said block, said extension also lying within the channel of said handle and having a secondary cylinder bore provided therein lengthwise thereof in spaced parallel relation to the rst mentioned bore, the exhaust ports of said rstment-ioned bore communicating with ports in the opposite ends of said secondary cylinder bore, a slide reciprocable in unison with said piston relative to said ports in said second-ary bore t-o open and close the same and having its opposite end portions extending from the ends of said bore and including portions of reduced diameter, and an elongated p ad holder disposed for reciprocation below said extension and having upward projections `on its opposite ends connected with the projecting end portions of said slide for reciprocation in unisontherewith. n I l 12. A portable air driven' sander comprising anelongated cylinder block lhaving a cylinder bore extending lengthwise therethrough, said block having inlet ports spaced inwardly from the opposite ends Iand exhaust ports spaced farther inwardly trom said ends, a piston reciprocable in said cylinder and adapted to cover and uncover the exhaust ports alternately, valves slidable as pistons -in the opposite ends of said bore relative to and adapted to cover and uncover the intake ports alternately .and arranged to be engaged and moved outwardly by the piston, Ispring means normally urging the valves inwardly, an elongated handle of inverted channel shaped cross-section straddling said cylinder block and secured thereto, said cylinder block having a downward extension within the channel of said handle in which a secondary cylinder bore is provided in spaced parallel relation to the first mentioned bore, the exhaust ports of said first mentioned bore communicating with ports in the opposite ends of said secondary cylinder bore, a slide reciprocable relative to said ports in said secondary bore to cover and uncover the same and having portions extending from the opposite ends of said bore, means connecting the piston and slide to reciprocate in unison, end plates fastened to the opposite ends of said handle covering the opposite ends of the cylinder bore and serving as abutments for the spring means urging the valves inwardly, said end plates extending downwardly as for as the side walls of the handle to cooperate with the latter in enclosing the downward extension of said cylinder block, and an elongated pad holder reciprocable beneath the open bottom of said handle and operatively connected `at its opposite ends with the projecting ends of said side so as to reciprocate in unison therewith.

13. A portable ai driven sander comprising an elongated cylinder block having a cylinder bore extending lengthwise therethrough, said block having inlet ports spaced inwardly from the opposite ends and exhaust ports spaced farther inwardly from said ends, a piston reciprocable in said cylinder and adapted to cover and uncover the exhaust ports alternately, valves slidable as pistons in the opposite ends of said bore relative to and adapted to cover and uncover the intake ports alternately and arranged to be engaged and moved outwardly by the piston, spring means normally urging the valves inwardly, an elongated handle of inverted channel shaped cross-section st-raddling said cylinder block and secured thereto, said cylinder block having a downward extension of elongated form but shorter length than said cylinder block having its ends Vspaced inwardly alike from both ends of said block, said extension also lying within the lchannel of said handle and having a secondary cylinder bore provided therein lengthwise thereof in spaced parallel relation to the first mentioned bore, the exhaust ports of said iirst mentioned bore communicating with ports in the opposite ends ofsaid secondary cylinder bore, a slide reciprocable with said piston relative to said ports in said secondary bore to open and close the same and having its opposite end portions extending from the ends of said bore rand including portions of reduced diameter, end plates fastened to the opposite ends of said handle covering the opposite ends of the cylinder bore and serving as abutments for the spring means u-rging the valves inwardly, said end plates exltending downwardly as far as the side walls of the handle to cooperate with the latter in enclosing the downward extension of said cylinder block, and an elongated pad holder disposed for reciprocation below said extension and having upward projections on it-s opposite ends connected with the projecting end p ortions of said slide for reciprocation in unison therewith.

14. A portable air driven sander comprising an elongated cylinder block having 4a cylinder bore extending lengthwise therethrough, said block having inlet ports spaced inwardly from the opposite ends and exhaust ports spaced farther inwardly from said ends, a piston reciprocable in said cylinder and adapted to cover and un cover the exhaust ports alternately, valves slidable aspistons in the opposite ends of said bore relative to and adapted to cover and uncover the intake ports alternately and arranged to be engaged and moved outwardly by the piston, spring means normally urging the valves inwardly, an elongated handle of inverted channel shaped cross-section 'straddling said cylinder block providing passages between the inner side thereof and the outside of said cylinder block which communicate with the exhaust ports so vas to direct exhaust air out of the open bottom of said `handle, a bushing threaded in the cylinder block through a hole provided in the top cross-portion of the handle, a headed screw in said hole threaded inside the bushing having the head portion received in a counterbore in the hole in the handle, and a member reciprocable beneath the open bottom of said handle and operatively connected with said piston to reciprocate in unison with it.

l5. A sander as set forth in claim 14, wherein the bushing has an inner end wall vin which a hole is provided covered by a screen disposed inside the bushing, and compressible lubricant absorbent material is disposed in the bushing and compressed between the inner end of the screw and the screen.

16. A reciprocating hand tool comprising an openended elongated cylinder having ai-r linlet and outlet ports in spaced relation in the opposite end portions, a piston reciprocable in said cylinder and adapted to cover and uncover the outlet ports alternately, valves slidable as pistons relative to and adapted'to cover and uncover the inlet ports alternately and arranged to be engaged and moved outwardly by the piston against the action of return springs which normally urge said valves inwardly, an elongated handle of inverted channel-shaped cross-section open at opposite ends straddling said cylinder and providingl passages between the inner side thereof and the outside of said cylinder which communicate with the outlet ports so as to direct exhaust air downwardly out of the open bottom of said handle, end plates having recesses provided therein in register with the ends of the cylinder in which bushings are received, said bushings having reduced portions entered in the opposite ends of said cylinder whereby to locate said end plates in rigid relationship to the ends of said cylinder, said Vend plates being secured to and closing the ends of said handle, said end plates falso providing abutments for the valve return springs and having air vent openings provided therein in register with said valves and bushings, and Ia work engaging member operatively connected with said piston to reciprocate in unison therewith relative to the handle.

References Cited in the tile of this patent UNITED STATES PATENTS 2,681,042 Larson June 15, 1954 FOREIGN PATENTS 632,557 Great Britain NOV. 28, 1949 

